[RFC PATCH v1 06/18] x86: Provide general kernel support for memory encryption

Tom Lendacky
2016-04-26T22:46:14Z

Adding general kernel support for memory encryption includes:
- Modify and create some page table macros to include the Secure Memory
Encryption (SME) memory encryption mask
- Update kernel boot support to call an SME routine that checks for and
sets the SME capability (the SME routine will grow later and for now
is just a stub routine)
- Update kernel boot support to call an SME routine that encrypts the
kernel (the SME routine will grow later and for now is just a stub
routine)
- Provide an SME initialization routine to update the protection map with
the memory encryption mask so that it is used by default

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
arch/x86/include/asm/fixmap.h | 7 ++++++
arch/x86/include/asm/mem_encrypt.h | 18 +++++++++++++++
arch/x86/include/asm/pgtable_types.h | 41 ++++++++++++++++++++++-----------
arch/x86/include/asm/processor.h | 3 ++
arch/x86/kernel/espfix_64.c | 2 +-
arch/x86/kernel/head64.c | 10 ++++++--
arch/x86/kernel/head_64.S | 42 ++++++++++++++++++++++++++--------
arch/x86/kernel/machine_kexec_64.c | 2 +-
arch/x86/kernel/mem_encrypt.S | 8 ++++++
arch/x86/mm/Makefile | 1 +
arch/x86/mm/fault.c | 5 ++--
arch/x86/mm/ioremap.c | 3 ++
arch/x86/mm/kasan_init_64.c | 4 ++-
arch/x86/mm/mem_encrypt.c | 30 ++++++++++++++++++++++++
arch/x86/mm/pageattr.c | 3 ++
15 files changed, 145 insertions(+), 34 deletions(-)
create mode 100644 arch/x86/mm/mem_encrypt.c

diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
index 8554f96..83e91f0 100644
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -153,6 +153,13 @@ static inline void __set_fixmap(enum fixed_addresses idx,
}
#endif

+/*
+ * Fixmap settings used with memory encryption
+ * - FIXMAP_PAGE_NOCACHE is used for MMIO so make sure the memory
+ * encryption mask is not part of the page attributes
+ */
+#define FIXMAP_PAGE_NOCACHE PAGE_KERNEL_IO_NOCACHE
+
#include <asm-generic/fixmap.h>

#define __late_set_fixmap(idx, phys, flags) __set_fixmap(idx, phys, flags)
diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index 747fc52..9f3e762 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -15,12 +15,21 @@

#ifndef __ASSEMBLY__

+#include <linux/init.h>
+
#ifdef CONFIG_AMD_MEM_ENCRYPT

extern unsigned long sme_me_mask;

u8 sme_get_me_loss(void);

+void __init sme_early_init(void);
+
+#define __sme_pa(x) (__pa((x)) | sme_me_mask)
+#define __sme_pa_nodebug(x) (__pa_nodebug((x)) | sme_me_mask)
+
+#define __sme_va(x) (__va((x) & ~sme_me_mask))
+
#else /* !CONFIG_AMD_MEM_ENCRYPT */

#define sme_me_mask 0UL
@@ -30,6 +39,15 @@ static inline u8 sme_get_me_loss(void)
return 0;
}

+static inline void __init sme_early_init(void)
+{
+}
+
+#define __sme_pa __pa
+#define __sme_pa_nodebug __pa_nodebug
+
+#define __sme_va __va
+
#endif /* CONFIG_AMD_MEM_ENCRYPT */

#endif /* __ASSEMBLY__ */
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 7b5efe2..fda7877 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -3,6 +3,7 @@

#include <linux/const.h>
#include <asm/page_types.h>
+#include <asm/mem_encrypt.h>

#define FIRST_USER_ADDRESS 0UL

@@ -115,9 +116,9 @@

#define _PAGE_PROTNONE (_AT(pteval_t, 1) << _PAGE_BIT_PROTNONE)

-#define _PAGE_TABLE (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | \
+#define __PAGE_TABLE (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | \
_PAGE_ACCESSED | _PAGE_DIRTY)
-#define _KERNPG_TABLE (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | \
+#define __KERNPG_TABLE (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | \
_PAGE_DIRTY)

/*
@@ -185,18 +186,30 @@ enum page_cache_mode {
#define __PAGE_KERNEL_IO (__PAGE_KERNEL)
#define __PAGE_KERNEL_IO_NOCACHE (__PAGE_KERNEL_NOCACHE)

-#define PAGE_KERNEL __pgprot(__PAGE_KERNEL)
-#define PAGE_KERNEL_RO __pgprot(__PAGE_KERNEL_RO)
-#define PAGE_KERNEL_EXEC __pgprot(__PAGE_KERNEL_EXEC)
-#define PAGE_KERNEL_RX __pgprot(__PAGE_KERNEL_RX)
-#define PAGE_KERNEL_NOCACHE __pgprot(__PAGE_KERNEL_NOCACHE)
-#define PAGE_KERNEL_LARGE __pgprot(__PAGE_KERNEL_LARGE)
-#define PAGE_KERNEL_LARGE_EXEC __pgprot(__PAGE_KERNEL_LARGE_EXEC)
-#define PAGE_KERNEL_VSYSCALL __pgprot(__PAGE_KERNEL_VSYSCALL)
-#define PAGE_KERNEL_VVAR __pgprot(__PAGE_KERNEL_VVAR)
-
-#define PAGE_KERNEL_IO __pgprot(__PAGE_KERNEL_IO)
-#define PAGE_KERNEL_IO_NOCACHE __pgprot(__PAGE_KERNEL_IO_NOCACHE)
+#ifndef __ASSEMBLY__
+
+#define _PAGE_ENC sme_me_mask
+
+/* Redefine macros to inclue the memory encryption mask */
+#define _PAGE_TABLE (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | \
+ _PAGE_ACCESSED | _PAGE_DIRTY | _PAGE_ENC)
+#define _KERNPG_TABLE (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | \
+ _PAGE_DIRTY | _PAGE_ENC)
+
+#define PAGE_KERNEL __pgprot(__PAGE_KERNEL | _PAGE_ENC)
+#define PAGE_KERNEL_RO __pgprot(__PAGE_KERNEL_RO | _PAGE_ENC)
+#define PAGE_KERNEL_EXEC __pgprot(__PAGE_KERNEL_EXEC | _PAGE_ENC)
+#define PAGE_KERNEL_RX __pgprot(__PAGE_KERNEL_RX | _PAGE_ENC)
+#define PAGE_KERNEL_NOCACHE __pgprot(__PAGE_KERNEL_NOCACHE | _PAGE_ENC)
+#define PAGE_KERNEL_LARGE __pgprot(__PAGE_KERNEL_LARGE | _PAGE_ENC)
+#define PAGE_KERNEL_LARGE_EXEC __pgprot(__PAGE_KERNEL_LARGE_EXEC | _PAGE_ENC)
+#define PAGE_KERNEL_VSYSCALL __pgprot(__PAGE_KERNEL_VSYSCALL | _PAGE_ENC)
+#define PAGE_KERNEL_VVAR __pgprot(__PAGE_KERNEL_VVAR | _PAGE_ENC)
+
+#define PAGE_KERNEL_IO __pgprot(__PAGE_KERNEL_IO)
+#define PAGE_KERNEL_IO_NOCACHE __pgprot(__PAGE_KERNEL_IO_NOCACHE)
+
+#endif /* __ASSEMBLY__ */

/* xwr */
#define __P000 PAGE_NONE
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 8d326e8..1fae737 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -22,6 +22,7 @@ struct vm86;
#include <asm/nops.h>
#include <asm/special_insns.h>
#include <asm/fpu/types.h>
+#include <asm/mem_encrypt.h>

#include <linux/personality.h>
#include <linux/cache.h>
@@ -207,7 +208,7 @@ static inline void native_cpuid(unsigned int *eax, unsigned int *ebx,

static inline void load_cr3(pgd_t *pgdir)
{
- write_cr3(__pa(pgdir));
+ write_cr3(__sme_pa(pgdir));
}

#ifdef CONFIG_X86_32
diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c
index 4d38416..3385377 100644
--- a/arch/x86/kernel/espfix_64.c
+++ b/arch/x86/kernel/espfix_64.c
@@ -193,7 +193,7 @@ void init_espfix_ap(int cpu)

pte_p = pte_offset_kernel(&pmd, addr);
stack_page = page_address(alloc_pages_node(node, GFP_KERNEL, 0));
- pte = __pte(__pa(stack_page) | (__PAGE_KERNEL_RO & ptemask));
+ pte = __pte(__pa(stack_page) | ((__PAGE_KERNEL_RO | _PAGE_ENC) & ptemask));
for (n = 0; n < ESPFIX_PTE_CLONES; n++)
set_pte(&pte_p[n*PTE_STRIDE], pte);

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index b72fb0b..3516f9f 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -28,6 +28,7 @@
#include <asm/bootparam_utils.h>
#include <asm/microcode.h>
#include <asm/kasan.h>
+#include <asm/mem_encrypt.h>

/*
* Manage page tables very early on.
@@ -42,7 +43,7 @@ static void __init reset_early_page_tables(void)
{
memset(early_level4_pgt, 0, sizeof(pgd_t)*(PTRS_PER_PGD-1));
next_early_pgt = 0;
- write_cr3(__pa_nodebug(early_level4_pgt));
+ write_cr3(__sme_pa_nodebug(early_level4_pgt));
}

/* Create a new PMD entry */
@@ -54,7 +55,7 @@ int __init early_make_pgtable(unsigned long address)
pmdval_t pmd, *pmd_p;

/* Invalid address or early pgt is done ? */
- if (physaddr >= MAXMEM || read_cr3() != __pa_nodebug(early_level4_pgt))
+ if (physaddr >= MAXMEM || read_cr3() != __sme_pa_nodebug(early_level4_pgt))
return -1;

again:
@@ -157,6 +158,11 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)

clear_page(init_level4_pgt);

+ /* Update the early_pmd_flags with the memory encryption mask */
+ early_pmd_flags |= _PAGE_ENC;
+
+ sme_early_init();
+
kasan_early_init();

for (i = 0; i < NUM_EXCEPTION_VECTORS; i++)
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 5df831e..0f3ad72 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -95,6 +95,13 @@ startup_64:
jnz bad_address

/*
+ * Enable memory encryption (if available). Add the memory encryption
+ * mask to %rbp to include it in the the page table fixup.
+ */
+ call sme_enable
+ addq sme_me_mask(%rip), %rbp
+
+ /*
* Fixup the physical addresses in the page table
*/
addq %rbp, early_level4_pgt + (L4_START_KERNEL*8)(%rip)
@@ -116,7 +123,8 @@ startup_64:
movq %rdi, %rax
shrq $PGDIR_SHIFT, %rax

- leaq (4096 + _KERNPG_TABLE)(%rbx), %rdx
+ leaq (4096 + __KERNPG_TABLE)(%rbx), %rdx
+ addq sme_me_mask(%rip), %rdx /* Apply mem encryption mask */
movq %rdx, 0(%rbx,%rax,8)
movq %rdx, 8(%rbx,%rax,8)

@@ -133,6 +141,7 @@ startup_64:
movq %rdi, %rax
shrq $PMD_SHIFT, %rdi
addq $(__PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL), %rax
+ addq sme_me_mask(%rip), %rax /* Apply mem encryption mask */
leaq (_end - 1)(%rip), %rcx
shrq $PMD_SHIFT, %rcx
subq %rdi, %rcx
@@ -163,9 +172,19 @@ startup_64:
cmp %r8, %rdi
jne 1b

- /* Fixup phys_base */
+ /*
+ * Fixup phys_base, remove the memory encryption mask from %rbp
+ * to obtain the true physical address.
+ */
+ subq sme_me_mask(%rip), %rbp
addq %rbp, phys_base(%rip)

+ /*
+ * The page tables have been updated with the memory encryption mask,
+ * so encrypt the kernel if memory encryption is active
+ */
+ call sme_encrypt_kernel
+
movq $(early_level4_pgt - __START_KERNEL_map), %rax
jmp 1f
ENTRY(secondary_startup_64)
@@ -189,6 +208,9 @@ ENTRY(secondary_startup_64)
movq $(init_level4_pgt - __START_KERNEL_map), %rax
1:

+ /* Add the memory encryption mask to RAX */
+ addq sme_me_mask(%rip), %rax
+
/* Enable PAE mode and PGE */
movl $(X86_CR4_PAE | X86_CR4_PGE), %ecx
movq %rcx, %cr4
@@ -416,7 +438,7 @@ GLOBAL(name)
__INITDATA
NEXT_PAGE(early_level4_pgt)
.fill 511,8,0
- .quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE
+ .quad level3_kernel_pgt - __START_KERNEL_map + __PAGE_TABLE

NEXT_PAGE(early_dynamic_pgts)
.fill 512*EARLY_DYNAMIC_PAGE_TABLES,8,0
@@ -428,15 +450,15 @@ NEXT_PAGE(init_level4_pgt)
.fill 512,8,0
#else
NEXT_PAGE(init_level4_pgt)
- .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+ .quad level3_ident_pgt - __START_KERNEL_map + __KERNPG_TABLE
.org init_level4_pgt + L4_PAGE_OFFSET*8, 0
- .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+ .quad level3_ident_pgt - __START_KERNEL_map + __KERNPG_TABLE
.org init_level4_pgt + L4_START_KERNEL*8, 0
/* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
- .quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE
+ .quad level3_kernel_pgt - __START_KERNEL_map + __PAGE_TABLE

NEXT_PAGE(level3_ident_pgt)
- .quad level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+ .quad level2_ident_pgt - __START_KERNEL_map + __KERNPG_TABLE
.fill 511, 8, 0
NEXT_PAGE(level2_ident_pgt)
/* Since I easily can, map the first 1G.
@@ -448,8 +470,8 @@ NEXT_PAGE(level2_ident_pgt)
NEXT_PAGE(level3_kernel_pgt)
.fill L3_START_KERNEL,8,0
/* (2^48-(2*1024*1024*1024)-((2^39)*511))/(2^30) = 510 */
- .quad level2_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE
- .quad level2_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
+ .quad level2_kernel_pgt - __START_KERNEL_map + __KERNPG_TABLE
+ .quad level2_fixmap_pgt - __START_KERNEL_map + __PAGE_TABLE

NEXT_PAGE(level2_kernel_pgt)
/*
@@ -467,7 +489,7 @@ NEXT_PAGE(level2_kernel_pgt)

NEXT_PAGE(level2_fixmap_pgt)
.fill 506,8,0
- .quad level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
+ .quad level1_fixmap_pgt - __START_KERNEL_map + __PAGE_TABLE
/* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */
.fill 5,8,0

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index ba7fbba..eb2faee 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -103,7 +103,7 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
struct x86_mapping_info info = {
.alloc_pgt_page = alloc_pgt_page,
.context = image,
- .pmd_flag = __PAGE_KERNEL_LARGE_EXEC,
+ .pmd_flag = __PAGE_KERNEL_LARGE_EXEC | _PAGE_ENC,
};
unsigned long mstart, mend;
pgd_t *level4p;
diff --git a/arch/x86/kernel/mem_encrypt.S b/arch/x86/kernel/mem_encrypt.S
index ef7f325..f2e0536 100644
--- a/arch/x86/kernel/mem_encrypt.S
+++ b/arch/x86/kernel/mem_encrypt.S
@@ -14,6 +14,14 @@

.text
.code64
+ENTRY(sme_enable)
+ ret
+ENDPROC(sme_enable)
+
+ENTRY(sme_encrypt_kernel)
+ ret
+ENDPROC(sme_encrypt_kernel)
+
ENTRY(sme_get_me_loss)
xor %rax, %rax
mov sme_me_loss(%rip), %al
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index f989132..21f8ea3 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -39,3 +39,4 @@ obj-$(CONFIG_NUMA_EMU) += numa_emulation.o
obj-$(CONFIG_X86_INTEL_MPX) += mpx.o
obj-$(CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS) += pkeys.o

+obj-$(CONFIG_AMD_MEM_ENCRYPT) += mem_encrypt.o
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 5ce1ed0..9e93a0d 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -23,6 +23,7 @@
#include <asm/vsyscall.h> /* emulate_vsyscall */
#include <asm/vm86.h> /* struct vm86 */
#include <asm/mmu_context.h> /* vma_pkey() */
+#include <asm/mem_encrypt.h> /* __sme_va() */

#define CREATE_TRACE_POINTS
#include <asm/trace/exceptions.h>
@@ -523,7 +524,7 @@ static int bad_address(void *p)

static void dump_pagetable(unsigned long address)
{
- pgd_t *base = __va(read_cr3() & PHYSICAL_PAGE_MASK);
+ pgd_t *base = __sme_va(read_cr3() & PHYSICAL_PAGE_MASK);
pgd_t *pgd = base + pgd_index(address);
pud_t *pud;
pmd_t *pmd;
@@ -659,7 +660,7 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code,
pgd_t *pgd;
pte_t *pte;

- pgd = __va(read_cr3() & PHYSICAL_PAGE_MASK);
+ pgd = __sme_va(read_cr3() & PHYSICAL_PAGE_MASK);
pgd += pgd_index(address);

pte = lookup_address_in_pgd(pgd, address, &level);
diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index f089491..77dadf5 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -21,6 +21,7 @@
#include <asm/tlbflush.h>
#include <asm/pgalloc.h>
#include <asm/pat.h>
+#include <asm/mem_encrypt.h>

#include "physaddr.h"

@@ -424,7 +425,7 @@ static pte_t bm_pte[PAGE_SIZE/sizeof(pte_t)] __page_aligned_bss;
static inline pmd_t * __init early_ioremap_pmd(unsigned long addr)
{
/* Don't assume we're using swapper_pg_dir at this point */
- pgd_t *base = __va(read_cr3());
+ pgd_t *base = __sme_va(read_cr3());
pgd_t *pgd = &base[pgd_index(addr)];
pud_t *pud = pud_offset(pgd, addr);
pmd_t *pmd = pmd_offset(pud, addr);
diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 1b1110f..7102408 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -68,7 +68,7 @@ static struct notifier_block kasan_die_notifier = {
void __init kasan_early_init(void)
{
int i;
- pteval_t pte_val = __pa_nodebug(kasan_zero_page) | __PAGE_KERNEL;
+ pteval_t pte_val = __pa_nodebug(kasan_zero_page) | __PAGE_KERNEL | _PAGE_ENC;
pmdval_t pmd_val = __pa_nodebug(kasan_zero_pte) | _KERNPG_TABLE;
pudval_t pud_val = __pa_nodebug(kasan_zero_pmd) | _KERNPG_TABLE;

@@ -130,7 +130,7 @@ void __init kasan_init(void)
*/
memset(kasan_zero_page, 0, PAGE_SIZE);
for (i = 0; i < PTRS_PER_PTE; i++) {
- pte_t pte = __pte(__pa(kasan_zero_page) | __PAGE_KERNEL_RO);
+ pte_t pte = __pte(__pa(kasan_zero_page) | __PAGE_KERNEL_RO | _PAGE_ENC);
set_pte(&kasan_zero_pte[i], pte);
}
/* Flush TLBs again to be sure that write protection applied. */
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
new file mode 100644
index 0000000..00eb705
--- /dev/null
+++ b/arch/x86/mm/mem_encrypt.c
@@ -0,0 +1,30 @@
+/*
+ * AMD Memory Encryption Support
+ *
+ * Copyright (C) 2016 Advanced Micro Devices, Inc.
+ *
+ * Author: Tom Lendacky <thomas.lendacky@amd.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/init.h>
+#include <linux/mm.h>
+
+#include <asm/mem_encrypt.h>
+
+void __init sme_early_init(void)
+{
+ unsigned int i;
+
+ if (!sme_me_mask)
+ return;
+
+ __supported_pte_mask |= sme_me_mask;
+
+ /* Update the protection map with memory encryption mask */
+ for (i = 0; i < ARRAY_SIZE(protection_map); i++)
+ protection_map[i] = __pgprot(pgprot_val(protection_map[i]) | sme_me_mask);
+}
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index bbf462f..c055302 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -1976,6 +1976,9 @@ int kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,
if (!(page_flags & _PAGE_RW))
cpa.mask_clr = __pgprot(_PAGE_RW);

+ if (!(page_flags & _PAGE_ENC))
+ cpa.mask_clr = __pgprot(pgprot_val(cpa.mask_clr) | _PAGE_ENC);
+
cpa.mask_set = __pgprot(_PAGE_PRESENT | page_flags);

retval = __change_page_attr_set_clr(&cpa, 0);